Hunt prevention and afterburner ignition detection circuits



Dec. 15, 1959 E. H. HECKMAN 2,916,872

HUNT PREVENTION AND AFTERBURNER IGNITIONDETECTION CIRCUITS Filed Feb. 13, 1956' Bin :1

Valve IINVENTOR.

BY Mu /4w 1 nited a e i 2,916,872 V HUNT PREVENTION AND AFTERBURNER' IGNITION DETECTION CIRCUITSM- t il Earl Herbert Heckman,

by mesne assignments, to the United States of America as represented bythe Secretary ofthe Navy Application February 13,1956,'Serial No. 565,278

1 Claim. (c1. 60--35.6)

This invention relates to a control for jet engines wherein a circuit, which prevents hunting when the exhaust nozzle is closed when the engine reaches military r.p.m., is combined with a circuit for detecting afterburner ignition.

In the operation of jet engines when military r.p.m.,is reached, the speed switch nozzle which will reduce the speed returning the speed switch to open the exhaust nozzle. The result of this is a hunt. This invention relates to a device for locking the relay controlling the exhaust nozzle in energized position by a switch controlled through the power lever. Thus, the hunt is prevented.

In jet engines equipped with an afterburner, the operator of the engine should know when the afterburner is ignited. This is generally accomplished by a blow-out switch. However, this switch has proven somewhat unreliable. It is presently proposed to place an additional switch in a circuit to be closed by the speed control when the throttle is in afterburner position.

It is an object of this invention to provide a control means in the circuit adjusting the speed control and exhaust nozzle of a jet engine so that a hunt is prevented upon reaching military r.p.m.

It is a further object of this invention to incorporate an afterburner ignition detection means in the circuit with the military speed switch.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing.

The drawing is a schematic illustration of the invention which is a part of a complete control circuit.

Referring to the drawing there is disclosed a power control lever 1 which regulates the speed of the engine. Rotation of lever 1 in a counter-clockwise direction, as shown by the arrow, about the pivot increases the engine speed by increasing the fuel supply to the engine by opening a fuel valve (not shown) to which the lever is operatively connected in a conventional manner as is well known in the art. A typical fuel valve is shown in US. Patent No. 2,658,340 to H. Cohen. The switch 2 is a speed switch responsive to the r.p.m. of the engine and actuated by some well known means, as a governor, and has two operative positions, one indicating below military r.p.m. and the other indicates at or above military r.p.m. When military r.p.m. is reached, the speed switch 2 closes on the above military speed contact and energizes coil 3 of a relay which closes its normally open contact 4 and switch 16 regulating the exhaust nozzle. When switch 16 closes, the battery 17 energizes solenoid 18 which closes the exhaust nozzle through its controller 19. Under ordinary circumstances this may result in a loss of speed and a drop in r.p.m. which would release switch 2 to the below military r.p.m. position opening the contact 16 and the exhaust nozzle. Thus, the hunt would prevail.

operates to close the exhaust Thej'al.fterburner of a ,Overland Park, Kans., assignor',

. 2 To, prevent the hunt, this inventionfincofporates a locking switch 5 connected in series with the relay holdontact 4. This switch is controlled by. the power er 1 and arranged to close when the lever 1 is ro- Ita'ted above 50 counter-clockwise as shown by the arrow. turbojet ordinarily may be ignited when engine spe'edis 90% of its maximumrecommended operational or military r.p.m.; 50 on the power lever quadrarit is within this permitted range. When the speed switchlfoperates to energizethe relay coil 3 and the power ever" is above 50, relay 3 remains energized by holding eontactfiand locking switch 5. The subsequent retarding o'fthe power lever 1 to a position belowv opens" the" switch 5 and control is returned tothe speed switch 2. I

In planes equipped with an afterburner, it is common to use a blow-out switch 6 to detect when the afterburner is ignited. Under ordinary conditions when the afterburner ignites, the switch 6 is actuated by engine pressure to the A/B (afterburning) position and energizes relay 7 and indicator 9. The relay is then locked in by its own contact or switch 8. However, this switch 6 has proven to be somewhat unreliable.

To detect the ignition of the afterburner, this invention incorporates a detection circuit to be controlled by the speed switch. For afterburner combustion, the engine is operated at military r.p.m. by moving the powerlever 1 to the left as shown by the arrow. At this speed, switch 2 is closed by the governor and relay coil 3 is energized, since the circuit through it is now complete. The relay is then locked in by its own contact 4,. since the circuit through the relay coil 3 and switch 5 is complete, switch 5 having been closed by the mechanical linkage 13 on movement of the power lever 1 to the above 50 position to get the engine at'military r.p.m. Switch 12 likewise is closed by the mechanical linkage 13 and relay coil 14 is energized closing the relays nor! mally open contact 10.

When the afterburner ignites, causing speed switch 2 to position.

the engine speed drops, move to its below military But contact 10 is closed, since relay coil 14 is now energized by the circuit having in it switches 5,

12 and 4, which are all closed, as explained above, and relay coil 7 is energized by the circuit having switch 10. The relay thus keeps its contact 8, or other contacts (as 30) which regulate the nozzle, closed without any regard to the position of the blow-out switch 6. An indicator 9 is included to show that the circuit is complete after the afterburner has been ignited.

Thus a hunt prevention and 'an afterburner detection circuit, which operates independently of the normal blowout switch, are incorporated with a common speed switch.

Obviously many modifications and variations of'the present invention are possible in the light of the above teachings. Itis therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is: v

Control apparatus for a jet engine equipped with an afterburner, a power lever, a governor responsive to the speed of the engine, and a variable exhaust area nozzle, comprising a source of electrical energy, a speed switch electrically connected across said source of energy and operatively connected to said governor for movement between two positions in response to the engine speed, one

of which positions is at and the other of which positions is below the military r.p.m. of said engine, a blow-out I switch a plurality of relays, a first of said relays having with said power lever to close when said lever is moved 3 to a predetermined position, holding contact in series with said locking switch which is closed when said relay coil is energized, said locking switch and holding contactbeing connected in parallel witlisaid speed switch so that said first relay coil remains energized when said power lever is set in said predetermined position and said speed switch moves to its below military r.p.m. position due to loss of engine speed when afte'rbur'ning is initiated, means operatively connected to saidjfirst relay for maintaining the effective exhaust area of said noz zle at a desired setting for afterburning operation,--a second switch operatively connected to be closed by said power lever when said lever is moved to said predetermined position, a second relay having its coil "connected in series with said second switch and said speed' switch when said speed switch is in its above military r.'p.m. position, said second relay having a consaid first relay having a i .4 I 1 tact connected in series wi the coil of the third of said relays and said speed switch when said speed switch is in its below military r.p.m. position, a third relay contact parallel connected with said blow-out switch between the coil of said third relay contact and said second switch when the afterburner is in operation and means to open said blow-out switch upon either interruption or cessation of afterbilrner combustion, means operative by said third relay for maintaining said nozzle at a desired effective area setting and means energized by said third relay for indicating ignition of the 'afterburner.

References Citedin the file of this patent .UNITED STATES PATENTS 2,737,775 Klauber Mar. 13, 1956 2,746,242 Reed May 22, 1956 2,766,580 Buerer et al. Oct. 16, 1956 

